GB1023179A - Fractionation of mixtures of agarose and agaropectin - Google Patents

Abstract

A process for the fractionation of mixtures of agarose and agaropectin comprises bringing the mixtures, while in aqueous colloidal solution, into admixture with polyethylene glycol of sufficient concentration to precipitate agarose, said concentration being a function of the molecular weight of the polyethylene glycol, and at a temperature above that at which gelling of the colloidal solution will occur during the precipitation and below the temperature at which substantial degradation of agarose will occur within the period at which it is subjected to said temperature, thereby producing a precipitate in which the ratio of agarose to agaropectin is higher than in the original mixture, and a residual liquid colloidal dispersion in which the ratio of agarose to agaropectin is lower than in the original mixture, and separating the precipitate from the said residual dispersion. The process is applicable to the fractionation of natural agars, prepurified agars, and crude agar extracts from seaweed. The precipitation may be effected at 80-90 DEG C., and the temperature then allowed to fall to 60-80 DEG C. before separation of the precipitate from the residual dispersion. The precipitate may be separated by filtration and washed with hot polyethylene glycol. The polyethylene glycol may itself be brought into aqueous solution. A concentrated agar solution may be treated in stages by initial mixing with sufficient polyethylene glycol to produce partial precipitation, together with lowering of the viscosity, followed by further addition of polyethylene glycol until a predetermined final concentration of polyethylene glycol is obtained. Further agar solution may be added to the reaction mixture, and the deficiency of polyethylene glycol corrected by addition of more polyethylene glycol in pure form or as an aqueous solution. When one precipitation step produces incomplete fractionation, the fractionation may be carried out in stages. Fractional precipitation may be effected by increasing the precipitant concentration continually or in stages, to yield agarose fractions of different gel strengths. Any precipitate formed may be re-dissolved and re-precipitated to ensure complete fractionation or purification. The agaraose fractions may be further purified by electrophoresis. In one embodiment, the precipitation is carried out in presence of an electrolyte, such as sodium chloride or acetic acid. An agaropectin product may be precipitated from the residual colloidal dispersion, from which the agarose has been separated, by cooling the dispersion to below 20 DEG C. and adding acetone. The precipitated agaropectin may then be freed from polyethylene glycol by solvent extraction. Examples describe the fractionation of Spanish agar and Gelidium agar. The processing conditions are controlled by determination of gel strength, sulphur content, sulphate content, or by electroendormosis measurements.